The present invention relates generally to ring laser gyros and, more particularly, to a ring laser gyro comprising rotary oscillation apparatus.
In a ring laser gyro two electromagnetic waves in the form of monochromatic light beams are produced which are propagating in opposite directions. A rotation of the ring laser gyro about its input axis increases the path length for one light beam whereas the path length for the other light beam is reduced. The resulting path length change produces a frequency shift within each of the light beams since the oscillating frequency of the laser beams depends on the length of the laser path. Therefore the frequency difference is a function of the rotation rate.
At low rotational rates the frequency difference between both light beams becomes small and both light beams have the tendency to oscillate on the same frequency which effect is known as lock-in. In order to prevent this mutual interference of both light beams at low rotational rates it is well known to impart a rotary oscillation to the ring laser gyro so that the known lock-in effect is eliminated to a large extent.
In order to produce the rotary back and forth oscillation normally a mechanical oscillating device is provided which imparts a dither motion to the ring laser gyro. Such a device consists commonly of a spoked wheel which is inserted into a cut-out of the ring laser gyro where the hub of the wheel is stationarily mounted to a housing. Piezo-electrical elements mounted on the spokes produce an oscillating back and forth movement of the ring laser gyro when they are driven by according signals. An example of such a device may be taken from German Patent DE-OS 29 39 066 for a triangular laser structure and from GB-PS 15 36 081 for a rectangular laser structure.